webkitgtk-2.16.5HEADwebkitgtk-2.16.5master

1 files changed, 5 insertions, 18 deletions

diff --git a/Source/JavaScriptCore/dfg/DFGSSAConversionPhase.h b/Source/JavaScriptCore/dfg/DFGSSAConversionPhase.h
index 2fa5ff41a..03766896f 100644
--- a/Source/JavaScriptCore/dfg/DFGSSAConversionPhase.h
+++ b/Source/JavaScriptCore/dfg/DFGSSAConversionPhase.h
@@ -1,5 +1,5 @@
 /*
- * Copyright (C) 2013 Apple Inc. All rights reserved.
+ * Copyright (C) 2013, 2014 Apple Inc. All rights reserved.
  *
  * Redistribution and use in source and binary forms, with or without
  * modification, are permitted provided that the following conditions
@@ -23,10 +23,7 @@
  * OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY OF SUCH DAMAGE. 
  */
 
-#ifndef DFGSSAConversionPhase_h
-#define DFGSSAConversionPhase_h
-
-#include <wtf/Platform.h>
+#pragma once
 
 #if ENABLE(DFG_JIT)
 
@@ -36,10 +33,9 @@ class Graph;
 
 // Convert ThreadedCPS form into SSA form. This results in a form that has:
 //
-// - Roughly minimal Phi's. We use the Aycock & Horspool fixpoint for
-//   converting the CPS maximal Phis into SSA minimal Phis, with the caveat
-//   that irreducible control flow may result in some missed opportunities
-//   for Phi reduction.
+// - Minimal Phi's. We use the the Cytron et al (TOPLAS'91) algorithm for
+//   Phi insertion. Most of the algorithm is implemented in SSACalculator
+//   and Dominators.
 //
 // - No uses of GetLocal/SetLocal except for captured variables and flushes.
 //   After this, any remaining SetLocal means Flush. PhantomLocals become
@@ -84,12 +80,6 @@ class Graph;
 //   the caveat that the Phi predecessor block lists would have to be
 //   updated).
 //
-//   The easiest way to convert from this SSA form into a different SSA
-//   form is to redo SSA conversion for Phi functions. That is, treat each
-//   Phi in our IR as a non-SSA variable in the foreign IR (so, as an
-//   alloca in LLVM IR, for example); the Upsilons that refer to the Phi
-//   become stores and the Phis themselves become loads.
-//
 //   Fun fact: Upsilon is so named because it comes before Phi in the
 //   alphabet. It can be written as "Y".
 
@@ -98,6 +88,3 @@ bool performSSAConversion(Graph&);
 } } // namespace JSC::DFG
 
 #endif // ENABLE(DFG_JIT)
-
-#endif // DFGSSAConversionPhase_h
-